While, regarding a mobile communication system such as a portable telephone system, a service of the third generation method according to a CDMA (Code Division Multiple Access) method has been started already, investigations of a next generation mobile communication system capable of implementing higher-speed communication on the basis of an OFDMA (Orthogonal Frequency Division Multiple Access) method are proceeding (refer to Non-Patent Document 1 hereinafter described).
Therefore, the MIMO as a technique for increasing the transmission rate has been proposed as a reliable technique. An outline of a MIMO transmission system is depicted in FIG. 19. The MIMO transmission system depicted in FIG. 19 includes a sender apparatus 100 having a plurality of sending antennas (antenna systems) Tx#1, Tx#2, . . . , and Tx#n (n is an integer of 2 or more) and a receiver apparatus 200 having a plurality of receiving antennas (antenna systems) Rx#1, Rx#2, . . . , and Rx#n, MIMO is a spatial multiplex transmission technique wherein different data streams are set in parallel from the sending antennas Tx#i (i=1˜n) to increase the transmission capacity in proportion to the number n of the sending antennas. The different sending antennas Tx#i are disposed so as not to have correlation with each other, and the data streams sent from the sending antennas Tx#i individually pass along fading propagation paths independent of each other and are received by the receiving antennas Rx#i in a spatially mixed state with other different data streams.
As an implementation example of such a MIMO transmission system as described above, for example, as depicted in FIG. 20, a method is available wherein a stream process is carried out independently for each antenna. For example, PARC (Per Antenna Rate Control) wherein pre-coding (Precoding) is not carried out (refer to Non-Patent Document 2 hereinafter described), PSRC (Per Stream Rate Control) wherein pre-coding is carried out (refer to Non-Patent Document 3 hereinafter described) and so forth are available.
In particular, the system depicted in FIG. 20 includes, for example, the sender apparatus 100 and the receiver apparatus 200. The sender apparatus 100 includes, for example, a stream separation section 101, a CRC addition section 102 and a coding section 103 as well as a HARQ processing section 104 for each sending stream, a sending section 105 and a re-sending controlling section 106. And the receiver apparatus 200 includes, for example, a signal separation and synthesis section 201, a HARQ processing section 202 and a CRC calculation section 203 for each received stream, an ACK/NACK decision section 204 and a stream synthesis section 205. It is to be noted that a reference character ATR represents a receiving antenna of the sender apparatus 100 and another reference character ATT represents a sending antenna of the receiver apparatus 200, and, in the present example, it is represented for the convenience of illustration that an ACK/NACK (Acknowledgement/Negative Acknowledgement) signal (acknowledgment signal) is sent from the sending antenna ATT and received by the receiving antenna ATR.
Then, the sender apparatus (hereinafter referred to sometimes as sender side) 100 operates, for example, in accordance with a flow chart depicted in FIG. 21, and the receiver apparatus (hereinafter referred to sometimes as receiver side) 200 operates, for example, in accordance with a flow chart depicted in FIG. 22.
In particular, in the sender apparatus 100, sending data are separated into sending streams of the antenna systems Tx#i by the stream separation section 101 (step A1) and CRC (Cyclic Redundant Check) codes for error detection are added to each of the sending streams of the antenna systems Tx#i by the CRC addition section 102 (step A2), and coding of the data streams is carried out for bit error correction by the coding section 103 and a HARQ (Hybrid Automatic Repeat request) process is carried out for re-sending control by the HARQ processing section 104 (step A4). Then, a sending antenna Tx#i for sending a HARQ block (process) is selected by the sending section 105, and the HARQ block is modulated and then sent to the receiver apparatus 200. Here, while, where pre-coding is used (in case of yes at step A5), each process can select a plurality of sending antennas Tx#i, in case of the PARC (in case of no at step A5), each process is sent from a sending antenna Tx#i determined in advance.
On the other hand, in the receiver apparatus 200, as depicted in FIG. 22, if a signal sent from the sender apparatus 100 is received by the receiving antennas Rx#i, then separation and synthesis of the received signals is carried out by the signal separation and synthesis section 201 (step B1), and it is decided whether or not each of the received signals (processes) is a re-sent process (step B2). As a result, if the received signal is a re-sent process (in case of yes at step B2), then the receiver apparatus 200 synthesizes the signal received in the present reception cycle and a received signal of the same process received and stored in the preceding reception cycle by means of the HARQ processing section 202 (step B3), and checks CRC codes added to each process by means of the CRC calculation section 203 to detect bit errors (step B4). It is to be noted that, where the process received in the present reception cycle is not a re-sent process (in case of no at step B2), synthesis by the HARQ process section 202 is not carried out but bit error detection by the CRC calculation section 203 is carried out (step B4).
Then, if a bit error is detected by the ACK/NACK decision section 204 (in case of yes at step B5), then the received process is retained and a NACK signal is sent as a reply to the sender apparatus 100 through the sending antenna ATT (step B6), but, if no bit error is detected (in case of no at step B5), then an ACK signal is sent as a reply to the sender apparatus 100 through the sending antenna ATT and the process is passed to an upper layer (step B7). It is to be noted that the received signals of the streams from which no error is detected are synthesized finally by the stream synthesis section 205 and then outputted.
In such series of processes as described above, an important function for high-speed communication is the HARQ. The HARQ is an ARQ method which is a combination of automatic re-sending request (ARQ) and error correction coding (FEC: Forward Error Correction). In particular, on the sender side 100, a block of information bits is error correction coded with a parity bit for error detection added, and all or some of the codes. If re-sending occurs, then all or some of coding bits of the current block are sent.
On the receiver side 200, the synthesis process is carried out for individually corresponding bits of an existing block to a re-sent block, and error correction and error detection process are carried out again using the synthesis block obtained as a result of the synthesis process. In this manner, the receiver side 200 repetitively carries out ACK/NACK reply sending to the sender side 100 and trial of a decoding process by re-sending until block errors are eliminated within a range of a predetermined number of times as an upper limit.
In the next generation mobile communication, particularly an N-channel Stop-and-Wait ARQ is applied (refer to Non-Patent Document 4 hereinafter described). Here, N represents an integer and represents the number of blocks (number of processes) which can be sent at the same time. For each of processes sent at the same time, re-sending control by the Stop and Wait is carried out.
An outline of the N-channel Stop-and-Wait ARQ is illustrated in FIG. 23.
Each process is sent within a unit interval of wireless transmission (TTI: Transmission Time Interval) and is identified with an identifier given as a process number N. In the case of FIG. 23, the process number N is N=5 (0˜4), and accordingly, the case of FIG. 23 corresponds to a case of 5-channel Stop-and-Wait ARQ. It is to be noted that, while it is depicted in FIG. 23 that a process number is added to the data part of each process for the convenience of illustration, actually a process number is sent with a controlling channel and no process number is added to the data part of each process. In particular, a process number is annexed to and sent together with the data part of each process (this similarly applies to the following description).
If the receiver apparatus 200 receives a process from the sender apparatus 100, then it carries out error detection in such a manner as described above. Here, if an error occurs with processes [1], [3] and [4] but no error occurs with processes [0] and [2], then regarding the processes [0] and [2] with which no error occurs, an ACK signal is sent as a reply to the sender apparatus 100, but regarding the processes [1], [3] and [4] with which an error occurs, a NACK signal is sent as a reply to the sender apparatus 100 after they are retained into a memory (not depicted). While also a reply of the ACK/NACK signal is sent with the controlling channel, in this instance, the process number need not be sent back.
The receiver apparatus 200 adjusts the reply sending timing for each process and sends the ACK/NACK signal as a reply so that the sender apparatus 100 can identify to which process the ACK/NACK signal responds. Although, if the sender apparatus 100 receives an ACK signal, then sending of a new process is carried out, at this time, a process number which is not used in five processes in the past may be added arbitrarily including time at which the process number is added (in FIG. 23, process numbers which are not used are added in an ascending order).
On the other hand, although, if the sender apparatus 100 receives a NACK signal, then re-sending of a process with which an error occurs is carried out, at this time, a process number same as the process number in the preceding cycle is added. After the re-sending, the receiver apparatus 200 recognizes the process number to decide with which process the received process should be synthesized. In particular, if the processes [1], [3] and [4] which are re-sent processes are received, then the received processes [1], [3] and [4] are packet-synthesized with the processes [1], [2] and [3], respectively, which individually have process numbers same as those retained upon NACK signal sending in the preceding cycle. After the synthesis, the CRC codes are checked, and if the processes are successfully received correctly, then the ACK is sent as a reply to the sender apparatus 100. On the other hand, if an error occurs, then the process after the synthesis is retained and the NACK signal is sent as a reply again to the sender apparatus 100.
It is to be noted that, while two types of representative methods are available as a synthesis method, any of the synthesis methods may be utilized in the present invention. One of the synthesis methods is a type of a synthesis method wherein data fully same as that upon former sending is re-sent upon re-sending and a received signal upon former sending and another received signal upon re-sending are synthesized with each other to carry out production of data to be decoded, and the other one of the synthesis methods is a type of a synthesis method wherein a puncturing pattern of data after coding is changed upon re-sending to send bits which are not sent till then and a received signal upon former sending and another received signal upon re-sending are synthesized with each other to decrease the equivalent coding ratio so that the error correction capacity (coding gain) is enhanced. The latter technique is called IR (Incremental Redundancy).
Such process processing as described above is carried out in a similar manner irrespective of difference of the PARC or the pre-coding. Therefore, description is continuously given below taking the PARC as an example.
A manner of the N-channel Stop-and-Wait ARQ where the sender apparatus 100 and the receiver apparatus 200 are ready for the PARC is illustrated in FIG. 24.
Since the CRC addition, coding and HARQ processes are carried out independently for each antenna in the PARC as described above, an independent number is added also as a HARQ process number. In FIG. 24, a manner (refer to arrow marks of broken lines) is illustrated wherein re-sending occurs with the processes [1], [3] and [4] sent from the sending antenna Tx#1 and with the process [1] sent from the sending antenna Tx#2. In such a case as just described, since the HARQ is carried out for each antenna system as described above, re-sending control is carried out independently for each antenna system. It is to be noted that an addition method of the process number is carried out in accordance with a rule similar to that in FIG. 23.
Further, in the MIMO transmission in the next generation mobile communication system, in order to allow data signals sent from the different sending antennas Tx#i to be separated and synthesized among the sending antennas Tx#i, the sender apparatus 100 sends an antenna identification signal (for example, a pilot signal or a scrambling code).
An example of pilot signal addition where the two sending antennas of the sender apparatus 100 are used is depicted in FIG. 25. As depicted in (1) and (2) of FIG. 25, the pilot signal (R: Reference Symbol) is added in the same time series but indifferent frequency series between the antenna systems Tx#1 and Tx#2. The receiver apparatus 200 refers to the pilot signal to separate a signal of the antenna system Tx#1 from the received signal by the antenna system Rx#1 of the receiver apparatus 200 and separates a signal of the antenna system Tx#2 from the received signal by the antenna systems Rx#2 of the receiver apparatus 200, and then synthesizes the separated signals with each other to restore the sent stream (process). Further, association between the antenna systems and the pilot signals is sent with notification information.
Non-Patent Document 1: “3GPP TR25.913 V7.3.0 Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN) (Release 7),” 3GPP (France), March 2006
Non-Patent Document 2: Lucent, “Improving MIMO throughput with per-antenna rate control (PARC),” 3GPP (France), August 2001
Non-Patent Document 3: Lucent, “Per Stream Rate Control with Code Reuse TxAA and APP Decoding for HSDPA,” 3GPP (France), September 2002
Non-Patent Document 4: “3GPP TR25.814 V7.4.0 Physical Layer Aspects for evolved Universal Terrestrial Radio Access (UTRA) (Release 7),” 3GPP (France), June 2006